WASHINGTON — Hillary Rodham Clinton suspended her pioneering campaign for the presidency on Saturday and summoned supporters to use "our energy, our passion, our strength" to put Barack Obama in the White House.

"I endorse him and throw my full support behind him," said the former first lady, delivering the strong affirmation that her one-time rival and other Democratic leaders hoped to hear after a bruising campaign.

Amid tears from her supporters, Clinton issued a call for unity that emphasized the cultural and political milestones that she and Obama, the first black to secure a presidential nomination, represent.

"Children today will grow up taking for granted that an African-American or a woman can, yes, become the president of the United States," she said.

For Clinton and her backers, it was a poignant moment, the end of an extraordinary run that began with an air of inevitability and certain victory. About 18 million people voted for her; it was the closest a woman has come to capturing a nomination.

"Although we weren't able to shatter that highest, hardest glass ceiling this time, thanks to you, it has about 18 million cracks in it and the light is shining through like never before," she said in a speech before cheering supporters packed into the ornate National Building Museum, not far from the White House she longed to occupy, as president this time.

Indeed, her speech repeatedly returned to the new threshold her candidacy had set for women. In primary after primary, her support among women was a solid bloc of her coalition. She noted that she had received the support of women born before women could even vote.

But her main goal was to heal the rift in the party — one that cleaved Democrats in part by class, by gender and by race.

"The way to continue our fight now to accomplish the goals for which we stand is to take our energy, our passion, our strength and do all we can to help elect Barack Obama, the next president of the United States," she said.

"Today as I suspend my campaign, I congratulate him on the victory he has won and the extraordinary race he has run. I endorse him and throw my full support behind him and I ask of you to join me in working as hard for Barack Obama as you have for me," the New York senator said in her 28-minute address. Loud boos competed with applause.

Video: 'Personal, poignant and politically powerful'
With that and 13 other mentions of his name, Clinton placed herself solidly behind her Senate colleague from Illinois, who awaits Arizona Sen. John McCain in the general election. "We may have started on separate journeys but today, our paths have merged," Clinton said.

Obama, in a statement from Chicago where he was spending the weekend, declared himself "thrilled and honored" to have Clinton's support. He watched her speech on a computer over the Internet and placed a call to her afterwards.

"I honor her today for the valiant and historic campaign she has run," he said in his statement. "She shattered barriers on behalf of my daughters and women everywhere, who now know that there are no limits to their dreams. And she inspired millions with her strength, courage and unyielding commitment to the cause of working Americans."

Obama secured the 2,118 delegates needed to clinch the nomination Tuesday after primaries in South Dakota and Montana. Aides said Obama watched Clinton's speech live on the Internet. His campaign put a photo of the New York senator on its Web site and urged supporters to send her a message of thanks. Likewise, Clinton's Web site thanked her backers. "Support Senator Obama today," her Web page said. "Sign up now and together we can write the next chapter in America's story."

Party leaders welcome alliance
"As you may know, I was a boxer. And I've seen many fights go the distance," said Senate Democratic leader Harry Reid of Nevada. "But never have I seen one where everyone came out stronger — until now. Because of the unprecedented number of new voters and the tremendous amount of enthusiastic supporters all the Democrats brought to the primary process, we stand ready to win the White House in 2008."

Both Obama and Clinton stood to gain from the new collaboration.

Obama could use the women and blue-collar voters who flocked to Clinton's campaign. She could benefit from his prodigious fundraising to help retire a debt of as much as $30 million. Clinton loaned her campaign at least $11.4 million; by law only, she has until the summer Democratic convention to recoup it.

Clinton also has told colleagues she would be interested in joining Obama as his running mate. On Saturday, the Rev. Jesse Jackson, an Obama supporter, said she had made "a powerful case for her eligibility" to be on the ticket.

Joining Clinton on stage Saturday were her husband, the former president, and their daughter, Chelsea, to loud cheers from the crowd. When she spoke, they stepped away. Her mother, Dorothy Rodham, watched from the floor to the side of the stage and wiped away a tear.

In deciding to suspend her campaign, Clinton kept some options open. She gets to retain her delegates to the nominating convention this summer and she can continue to raise money. It also means she could reopen her campaign if circumstances change before the Denver convention, but gave no indication that was her intention.

As soon as Clinton finished speaking, some of the nearly 300 Democratic party leaders and elected officials across the country who had pledged their support to her as superdelegates released statements announcing they now back Obama. The switchers included some of Clinton's most high-profile supporters, including Michigan Gov. Jennifer Granholm, Maryland Sen. Barbara Mikulski and Maine Gov. John Baldacci.

Clinton supporters began lining up at dawn to attend the farewell address. A smattering of Obama backers showed up as well, saying they did so as a gesture of party unity.

As they awaited her arrival, campaign staffers milled the room, exchanging hugs and saying goodbye.

'A somber day'Clinton seemed almost buoyant in her address, feeding off the energy of a loud and appreciative crowd.

"Well, this isn't exactly the party I planned but I sure like the company," she said as she opened her speech.

Clinton backers described themselves as sad and resigned. "This is a somber day," said Jon Cardinal, one of the first in line. Cardinal said he planned, reluctantly, to support Obama in the general election. "It's going to be tough after being against Obama for so long," he said.

Republicans quickly launched a "Clinton vs. Obama" page on the Republican National Committee's Web site drawing attention to her criticism of Obama during the campaign.

President Bush praised the symbolism of the 2008 field.

"I thought it was a really good statement, powerful moment when a major political party nominates an African-American man to be their standard bearer," he said in an interview Friday with an Italian journalist. "And it's good for our democracy that that happened. And we also had a major contender being a woman. Obviously Hillary Clinton was a major contender. So I think it's a good sign for American democracy."